Density
Density (symbol: ρ'' - : ) is a measure of mass per unit of volume. Explained The higher an object's density, the higher its mass per volume. The average density of an object equals its total mass by its total volume. A denser object (such as ) will have less volume than an equal mass of some less dense substance (such as water). The 'SI unit''' of density is the (kg· ) : \rho = \frac{m}{V} where :ρ'' is the object's density (measured in kilograms per cubic metre) :''m is the object's total mass (measured in kilograms) :V'' is the object's total volume (measured in cubic metres) Under specified conditions of temperature and pressure, density of a fluid is defined as described above. Definitions However, the density of a solid material can be different, depending on exactly how it is defined. Take for example. If you gently fill a container with sand, and divide the mass of sand by the container volume you get a value termed ''loose . If you took this same container and tapped on it repeatedly, allowing the sand to settle and pack together, and then calculate the results, you get a value termed tapped or packed bulk density. Tapped bulk density is always greater than or equal to loose bulk density. In both types of bulk density, some of the volume is taken up by the spaces between the grains of sand. Also, in terms of making, density is affected by the melting and cooling processes. Loose granular , like sand, contains a lot of air and is not tightly packed, but when it has melted and starts to boil, the sugar loses its granularity and entrained air and becomes a fluid. When you mold it to make a smaller, compacted shape, the syrup tightens up and loses more air. As it cools, it contracts and gains moisture, making the already heavy candy even more dense. A more theoretical definition is also available. Density can be calculated based on crystallographic information and molar mass: : \mbox{density} = \frac{M \cdot N} {L \cdot a \cdot b \cdot c} where :M'' is molar mass :''N is the number of atoms in a unit cell :L'' is or number :''a, b, c are the The density with respect to temperature, T, has the following relation: : \frac{density(T1)} {density(T2)} = \frac{1 + C * T1} {1 + C * T2} where :C'' is the coefficient of cubic expansion. Experimentally density can be found by measuring the dry weight ( W_d ), the wet weight ( W_w ) and submersed weight ( W_s ), usually in water. : density = \frac{W_d * density of water} {W_w - W_s} Other units '''Density' in terms of the SI base units is expressed in terms of kilograms per cubic metre (kg·m−3). Other units fully within the SI include grams per cubic centimetre (g·cm−3) and megagrams per cubic metre (Mg·m−3). Since both the litre and the or metric ton are also acceptable for use with the SI, a wide variety of units such as kilograms per litre (kg·L−1) are also used. or , the units of density include s per (lb/ft³), pounds per cubic yard (lb/yd³), pounds per cubic inch (lb/in³), ounces per cubic inch (oz/in³), pounds per (for U.S. or imperial gallons) (lb/gal), pounds per U.S. (lb/bu), in some engineering calculations per cubic foot, and other less common units. The maximum density of pure water at a pressure of one standard is 999.972 kg·m−3; this occurs at a temperature of about 3.98 °C (277.13 K). Measurement of density A common device for measuring fluid density is a . A device for measuring absolute density of a solid is a . Highest density The most dense naturally occurring substance on is , at about 22650 kg·m−3. A table of densities of various substances: Note the low density of aluminium compared to most other metals. For this reason, aircraft are made of aluminium. Also note that air has a nonzero, albeit small, density. is the world's lightest solid. See also * : volumic mass *Standard temperature and pressure * (specific gravity) Category:Physics Category:Chemistry Category:Measurement